An electrocardiogram (ECG) is a very important tool in the diagnosis of heart disease and abnormalities in both children and adults. The new detection capabilities provided by recent advances in signal processing allow the possibility of obtaining valuable information from fetal heart electrical activity. The use of a fetal ECG (fECG) could lead to the early detection and monitoring of heart abnormalities providing better information throughout gestation and particularly perinatally.
However, obtaining an accurate fetal ECG is difficult due to the weaker fetal information obtained from the abdomen of the mother. Specifically, when multiple ECG electrodes are placed on the abdomen of the mother to gather the required ECG information, several obvious problems arise. The first is that the mother's ECG is present and is usually significantly larger than the ECG of the fetus. Second, if monitoring is being done late in pregnancy, uterine contractions may be present, which result in large electrical artifacts that obliterate or mask the fetal signal. Third, in many cases, the mother is experiencing discomfort and is unable to lie still, which creates large electrical muscle artifacts.
Presently, signal processing techniques exist, including the use of independent component analysis (ICA) algorithms, that are applied the input ECG signals obtained from the mother to provide clean waveforms that can be further processed. In many cases, the output from the ICA algorithm can be used to provide a signal for finding the fetal heart rate. Typically, one channel of the multi-channel abdominal maternal ECG leads is used for determining the fetal heart rate. The ICA algorithm is performed on a set of waveforms over an epoch having a determined length, such as 4 to 5 seconds. Although a particular channel from the ICA algorithm output can be used to identify fetal heart rate for the specific epoch, the fetal and maternal ECG signals oftentimes change channels from one epoch to the next. For the purposes of determining fetal heart rate, the channel jumping of the ICA output is a problem since a separated fECG signal may not be in the same waveform position from epoch to epoch. Additionally, automated techniques for identifying and monitoring the fetal ECG are further complicated by the changing channels of both the fetal and maternal signals over multiple epochs. Therefore, it becomes necessary to have a method and means to recognize which among the scrambled plurality of ICA output waveforms from any epoch is a fetal ECG, a maternal ECG, a uterine contraction or just noise. A need exists to make this determination for each epoch of a series of epochs such that the fetal ECG and maternal ECG can be monitored over an extended period of time.